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United States Patent |
5,559,755
|
Beam
|
September 24, 1996
|
Range finding device and method
Abstract
A method and apparatus for passively determining the range of a radiating
source that is in a state of motion with respect to an observer. In one
embodiment of the invention the range is determined in accordance with the
bearing rate of the radiating source, the bearing acceleration of the
radiating source, the frequency of the received radiation, the frequency
rate of the received radiation, and the velocity of the radiation through
a medium. In another embodiment of the invention the range is determined
in accordance with the bearing rate of the radiating source, the bearing
acceleration of the radiating source, the fractional frequency rate of the
received radiation, and the velocity of the radiation through the medium.
Inventors:
|
Beam; Jon P. (242 Nautilus Dr. #302, New London, CT 06320)
|
Appl. No.:
|
463000 |
Filed:
|
May 31, 1995 |
Current U.S. Class: |
367/118; 367/124 |
Intern'l Class: |
G01S 003/80 |
Field of Search: |
367/118,124
|
References Cited
U.S. Patent Documents
5357484 | Oct., 1994 | Bates et al. | 367/118.
|
5481505 | Jan., 1996 | Donald et al. | 367/130.
|
Primary Examiner: Eldred; J. Woodrow
Attorney, Agent or Firm: McGowan; Michael J., Kasischke; James M., Lall; Prithvi C.
Goverment Interests
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or for the
Government of the United States of America for governmental purposes
without the payment of any royalties thereon or therefore.
Claims
What is claimed is:
1. A method for determining a range of a radiating source relative to an
observer, the radiating source being in a state of motion relative to the
observer, comprising the steps of:
providing a bearing rate .theta. over a plurality of time periods;
providing a bearing acceleration .theta. over a plurality of time periods;
providing a frequency f.sub.r of the radiating source over a plurality of
time periods;
providing a frequency rate f.sub.r over a plurality of time periods;
providing a velocity c of the radiation relative to a medium through which
said radiation propagates over a plurality of time periods; and
determining the range r of said radiating source relative to said observer
in accordance with the expression:
##EQU13##
2. A method for determining a range of a radiating source relative to an
observer, the radiating source being in a state of motion relative to the
observer, comprising the steps of:
providing a bearing rate .theta. over a plurality of time periods;
providing a bearing acceleration .theta. over a plurality of time periods;
providing a fractional frequency rate F.sub.r over a plurality of time
periods;
providing a velocity c of the radiation relative to a medium through which
said radiation propagates over a plurality of time periods; and
determining the range r of said radiating source relative to said observer
in accordance with the expression:
##EQU14##
3. A device for determining a range of a radiating source relative to an
observer, the radiating source being in a state of motion relative to the
observer comprising:
a measurement unit detecting a bearing rate .theta., a bearing acceleration
.theta., a fractional frequency F.sub.r of the radiating source, and
information relating to a velocity of the radiation relative to a medium
through which the radiation propagates over a plurality of time periods;
a processing unit joined to said measurement unit for receiving measured
data, said processing unit comprising:
a first multiplier having a first input, a second input, and a first
multiplier output, said first multiplier being provided to receive said
radiation velocity at said first input and said fractional frequency rate
F.sub.r at said second input and multiply said first and second inputs for
output by said first multiplier output;
a second multiplier having a third input, a fourth input, and a second
multiplier output, said second multiplier being provided to receive said
fractional frequency rate F.sub.r, at a third input and said bearing
acceleration .theta. at a fourth input and multiply said third input and
said fourth inputs for output by said second multiplier output;
an amplifier having an amplifier input and an amplifier output, said
amplifier being provided to receive said bearing rate .theta. at said
amplifier input and double said amplifier input for output by said
amplifier output;
a third multiplier having a fifth input and a third multiplier output, said
third multiplier being provided to receive said bearing rate .theta. at
said fifth input and multiply said fifth input by itself for output by
said third multiplier output;
a first divider having a first dividend input connected to said second
multiplier output, a first divisor input connected to said amplifier
output, and a first divider output, said first divider being provided to
receive said second multiplier output at said first dividend input and
said amplifier output at said first divisor input and divide said first
dividend input by said first divisor input for output by said first
divider output;
a subtractor having a minuend input connected to said first divider output,
a subtrahend input connected to said third multiplier output, and a
subtractor output, said subtractor being provided to subtract said
subtrahend input from said minuend input for output by said subtractor
output; and
a second divider having a second dividend input connected to said first
multiplier output, a second divisor input connected to said subtractor
output, said second divider being provided to divide said second dividend
input by said second divisor output to provide a signal representing a
range at said second divider output.
4. A device for determining a range of radiating source relative to an
observer, the radiating source being in a state of motion relative to the
observer comprising:
a measurement unit detecting a bearing rate .theta., a bearing acceleration
.theta., a frequency f.sub.r and a frequency rate f.sub.r of the radiating
source, and information relating to a velocity of the radiation relative
to a medium through which the radiation propagates over a plurality of
time periods;
a processing unit joined to said measurement unit for receiving measured
data, said processing unit comprising:
a first multiplier having a first input, a second input, and a first
multiplier output, said first multiplier receiving said radiation velocity
at said first input and said frequency rate f.sub.r at said second input
and multiply said first and second inputs for output by said first
multiplier output;
a second multiplier having a third input, a fourth input, and a second
multiplier output, said second multiplier being provided to receive said
frequency rate f.sub.r at said third input and said bearing acceleration
.theta. at a fourth input and multiply said third input and said fourth
inputs for output by said second multiplier output;
an amplifier having an amplifier input and an amplifier output, said
amplifier being provided to receive said bearing rate .theta. at said
amplifier input and double said amplifier input for output by said
amplifier output;
a third multiplier having a fifth input and a third multiplier output, said
third multiplier being provided to receive said bearing rate .theta. at
said fifth input and multiply said fifth input by itself for output by
said third multiplier output;
a first divider having a first dividend input connected to said second
multiplier output, a first divisor input connected to said amplifier
output, and a first divider output, said first divider being provided to
receive said second multiplier output at said first dividend input and
said amplifier output at said first divisor input and divide said first
dividend input by said first divisor input for output by said first
divider output;
a fourth multiplier having a sixth input connected to said third multiplier
output, a seventh input receiving said radiation frequency f.sub.r, and a
fourth multiplier output, said fourth multiplier being provided to
multiply said sixth input by said seventh input for output by said fourth
multiplier output;
a subtractor having a minuend input connected to said first divider output,
a subtrahend input connected to said fourth multiplier output, and a
subtractor output, said subtractor being provided to subtract said
subtrahend input from said minuend input for output by said subtractor
output; and
a second divider having a second dividend input connected to said first
multiplier output, a second divisor input connected to said subtractor
output, said second divider being provided to divide said second dividend
input by said second divisor output to provide a signal representing a
range at said second driver output.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates generally to both apparatus and methods for
determining the range of a radiating source relative to an observer.
(2) Description of the Prior Art
Range finding is a process whereby the distance between an object and an
observer is determined. In general, the object may be a radiating source
or may be passive (i.e., an energy reflector). Of particular interest
herein is the case where the object is a passive source. Either a passive
object or a radiating source may be referred to as a target.
Range finding systems are either active or passive. Active systems
typically involve the transmission and reception of electromagnetic energy
(radar) or acoustic energy (sonar). A disadvantage of such active range
finding systems is that the transmission of such electromagnetic and
acoustic energy discloses the position or location of the observing ship
that transmits the ranging energy.
Passive sonar merely receives the acoustic energy generated from a distant
source and is only capable of giving information on the target bearing and
the acoustic frequency generated by the target.
An active sensor system, such as active sonar, can determine the distance
to an object directly by forming the product of (1) one half the sound
velocity and (2) the time interval from the instant of the transmission of
a ping until the instant of the arrival of the ping's echo from the
object.
A passive range finding system, such as passive sonar, can determine the
direction of a target (radiating source) and the frequency of the
radiation. Current techniques of passive ranging require that (1) special
conditions pertain or (2) additional information, other than frequency and
bearing data supplied by passive sonar, be known or that strong
assumptions be made.
Radio direction finding is another type of passive system which determines
only the bearing of a source of radio or electromagnetic emission. This is
usually accomplished by means of a directive receiving antenna.
There are several other techniques which may be applicable under certain
circumstances when the range of an acoustic radiating source is to be
determined. Bottom bounce ranging can be used when the bottom depth,
gradient and composition are known. Multipath ranging can be used if the
temperature profile, at the ocean location in question, is suitable.
Bottom bounce techniques require that (1) the combination of ocean
temperature profile, bottom depth and composition, and target range allow
reception of such a bounce and, (2) the bottom depth and orientation
vector be known in advance with reasonable accuracy. Often a tentative
range is calculated from a bottom bounce when the depth is known and a
horizontal bottom has been assumed.
Multipath ranging uses signals received from the source by reflection from
the surface, reflection from the bottom, and direct transmission. Range is
calculated from the delay time between receipt of the signals using the
temperature profile, and bottom and surface conditions.
Various prior art range finding apparatus are described in the following
documents. In Snowden, U.S. Pat. No. 3,304,409, Feb. 14, 1967, range is
determined as a function of the bearing .theta. of the target from an
observing ship, and measurements of the motion of the observing ship. In
Olsen, U.S. Pat. No. 3,947,804, Mar. 30, 1976, there is disclosed a
range/bearing computer that solves two trigonometric equations which are
indicative of the bearing and range of a target or radiating source. The
variables used in the equations are the time interval between the arrivals
of a wave front at different spaced locations, a constant voltage
proportional to the distance of separation of the spaced locations, the
velocity of propagation of the wave front, and the angle of inclination
formed by the intersection of a line drawn through the spaced locations
and a horizontal plane through one of the spaced locations.
None of the known methods or apparatus can directly determine the range to
the object of interest, the course and speed or track of the object, or
predict the position of the object at a given instant of time without
reference to surface or bottom conditions.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an apparatus and
method for passively determining the range of a radiating source relative
to an observer.
The advantages of the apparatus and method of this invention are that,
unlike the conventional techniques of determining the range of an acoustic
source, the apparatus and method do not require information resulting from
observer course changes or other special information, such as ocean bottom
depth or ocean floor topography. The apparatus and method also do not
require a favorable bottom composition. The apparatus and method are
favored by a temperature gradient appropriate for a direct target to
observer propagation path rather than the less common situation where a
temperature gradient is present allowing for a bottom bounce propagation
path.
A second advantage of this apparatus and method is that, unlike the
conventional techniques of determining the range of an electromagnetic
source, transmission of electromagnetic energy by the observer is not
required since this apparatus and method passively determines range.
Important aspects of the invention are that the frequency of a radiating
source, the frequency rate (the rate at which frequency changes with
time), the bearing rate, and the bearing acceleration, are used in
determining the range of the radiating source, or target, from the
observer. The apparatus and method of the invention utilize the velocity
of the radiated wave (electromagnetic or acoustic) relative to the medium
through which the radiation propagates. The velocity at which
electromagnetic and acoustic waves propagate depends on the medium through
which the waves propagate. The wave propagation velocity, hereafter
referred to as c, can be calculated by many well known methods from data
relating to the density of the medium.
In accordance with a first apparatus and method of the invention, the
process of determining the range of a radiating source from an observer is
accomplished by using the following information: the bearing rate of the
radiation source, the bearing acceleration of the radiating source, the
frequency of the radiation received from the radiating source, the
frequency rate and the radiation velocity. This information is processed
such that the result represents the range of the radiating source relative
to the observer.
In accordance with a second apparatus and method of the invention, the
process of determining the range of a radiating source relative to an
observer is accomplished by using the following information: bearing rate
of the radiating source, the bearing acceleration of the radiating source,
the fractional frequency rate of the radiating source and the radiation
velocity.
This invention addresses the common case wherein there is change in both
the bearing and the range of the radiating source, or target, relative to
the observer. Typically the target and the observer are both in motion.
The combination of the separate states of motion of the target and the
observer results in a change in the bearing and in the range of the target
from the observer. Either the target or the observer but not both can be
stationary relative to an absolute coordinate system, such as a geographic
coordinate system fixed to the earth for terrestrial applications. The
source must radiate some form of periodic radiation, which radiation may
be either acoustic, electromagnetic, or gravitational waves.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the invention and many of the attendant
advantages thereof will be readily appreciated and better understood by
reference to the following detailed description, when considered in
conjunction with the accompanying drawings, wherein:
FIG. 1 is a block diagram of an overall range finding system;
FIG. 2a is a flow chart illustrating a method of the invention using
frequency and frequency rate;
FIG. 2b is a block diagram of an apparatus that utilizes the frequency and
the frequency rate of the radiating source to determine range;
FIG. 3a is a flow chart illustrating an alternate method of the invention
using a fractional frequency rate; and
FIG. 3b is a block diagram of an alternate apparatus that utilizes the
fractional frequency rate of the radiating source to determine range.
DESCRIPTION OF THE PREFERRED EMBODIMENT
This invention is applicable to the case wherein there exists a continuous
relative motion between a radiating source, also referred to as a target,
and the observer, such that there is a change in both the bearing and the
range of the radiating source relative to the observer. If a radiating
source moves in a direction toward or away from a stationary observer,
without causing a change in bearing, then the range cannot be determined.
Similarly, if the movement of the radiating source results in a bearing
change, but not a range change, then range cannot be determined. As an
example, if a radiating source is circling an observer then the range
cannot be determined because the bearing of the source changes but the
range of the source does not change.
The motion of the radiating source relative to the observer need not be
purely rectilinear, wherein rectilinear motion is considered to be a
motion having a constant speed and direction. In nautical or atmospheric
applications for example, the normal incidental variation in course and
speed due to atmospheric or oceanic conditions does not make the method
unreliable. To obtain a reliable figure for the range from the observer to
the source, the first method requires sufficiently accurate estimates of
bearing rate, bearing acceleration, frequency, and frequency rate. The
alternate method requires accurate estimates of bearing rate, bearing
acceleration, and fractional frequency rate. Both methods require that the
target maintain an approximately steady course and speed over the time
interval of a few cycles of the radiation.
If measurements of bearing and frequency of the radiating source are made
at regular intervals of time, then the range can be determined for each
measurement period. Averaging the determined range estimates over several
measurement periods yields improved range estimates. The source need only
maintain approximately rectilinear motion over the duration of the
averaging interval.
As is shown in FIG. 1, a target 1 emits radiation shown here as rays 2
which propagates through a medium 3. By example, medium 3 can be water,
air, or a vacuum. An observer 4 includes a measurement unit 5 and a
processing unit 6. In FIG. 1, target 1 and observer 4 are shown in motion
with respect to one another with the direction of target 1 motion being
indicated by an arrow A, and the motion of observer 4 being indicated by
an arrow B. Measurement unit 5 is responsive to radiation 2 to provide
information expressive of the radiation frequency, the bearing of target 1
with respect to observer 4, and the velocity of radiation 2 through medium
3 to processing unit 6 along data path 7. Processing unit 6 is responsive
to the information provided by the measurement unit 5 to provide an
estimate of a range r of the target 1 with respect to the observer 4 in
accordance with the method and apparatus of the current invention. Both
measurement unit 5 and processing unit 6 can include apparatus for
smoothing their respective output signals via a moving average or other
well known method to eliminate rapid fluctuations in the output data.
The first embodiment of the processing unit 6 of this invention,
illustrated in FIGS. 2a and 2b, receives the following input data from the
measurement unit 5:
.alpha.: the estimate of the radiation velocity in the medium;
.theta.: the bearing rate (the change in bearing per unit of time);
.theta.: the bearing acceleration (the change in bearing rate per unit of
time);
f.sub.r : the frequency of the radiation received from the source; and
f.sub.r : the frequency rate (the change in frequency per unit of time).
The second embodiment of the processing unit 6, illustrated in FIGS. 3a and
3b, receives the following input data from the measurement unit 5:
.alpha.: the estimate of the radiation velocity in the medium;
.theta.: the bearing rate (as defined above);
.theta.: the bearing acceleration (as defined above); and
F.sub.r : the fractional frequency rate (the frequency rate
divided by the frequency of the radiation received from the radiating
source).
Important aspects of the invention are (1) the utilization of the frequency
and the frequency rate of the received radiation (the embodiment of FIGS.
2a and 2b), and (2) the utilization of the fractional frequency rate of
received radiation (the embodiment of FIGS. 3a and 3b). Other equally
important aspects of the invention are the utilization, by both
embodiments of the invention, of the bearing rate, the bearing
acceleration, and the speed of the radiation.
When there is a radial component (i.e., along a line of sight between the
source and the observer) to the relative velocity between a radiating
source and an observer, the frequency of the radiation seen by the
observer will be greater than the radiated frequency if the range is
decreasing, and less than the radiated frequency if the range is
increasing. The frequency difference, or shift, between the source
frequency and the observed frequency that is due to the radial velocity
between the source and observer is referred to as a Doppler shift.
The Doppler frequency shift is expressed as
##EQU1##
where V.sub.r is the radial velocity of the radiating source and the
observer, .lambda. is the wavelength of the transmitted radiation, f.sub.t
is the frequency of the transmitted radiation, and c is the speed of the
wave relative to the medium. Therefore, the frequency f.sub.r received by
the observer is expressed as
##EQU2##
wherein the plus sign is applicable to a radiation source and an observer
that are approaching one another, and the minus sign is applicable to a
radiating source and an observer that are moving away from one another.
Because of the Doppler effect, the frequency of the received radiation
changes per unit of time. Therefore, the frequency rate is expressed as
##EQU3##
where .DELTA.f.sub.r /.DELTA.t equals the change in the received frequency
of the radiating source per unit time;
f.sub.r1 is the frequency of the received radiation at t.sub.1 ; and
f.sub.r2 is the frequency of the received radiation at t.sub.2 and is
greater than or less than f.sub.r1 due to the Doppler effect.
A Doppler frequency shift appears if there is a radial motion between a
source and the observer. However, the existence of a Doppler shift, in and
of itself, is not a sufficient condition for the operation of the
apparatus and method of this invention. There must also exist a bearing
rate .theta. (motion across the line of sight) and a bearing acceleration
.theta.. A constant velocity motion across the line of sight guarantees a
bearing acceleration. In the case where the source is moving in a circle
about the observer, there is no bearing acceleration, but the source
velocity is constantly changing in direction.
The first method illustrated in the flow chart of FIG. 2a, and the
corresponding apparatus illustrated in FIG. 2b, utilize the frequency
f.sub.r and the frequency rate f.sub.r in determining the range of the
radiating source relative to the observer.
At Block A of FIG. 2a there is provided a set of input data. The set of
input data is comprised of the velocity c of the radiation relative to the
medium, the bearing rate .theta. of the radiating source, the bearing
acceleration .theta. of the radiating source, the frequency f.sub.r of the
received radiation, and the frequency rate f.sub.r of the radiating
source.
At Block B the following sub-steps are performed: (B1) multiply c times
f.sub.r to form cf.sub.r ; (B2) multiply f.sub.r times .theta. to form
f.sub.r .theta.; (B3) multiply .theta. times 2 to form 2.theta.; and (B4)
multiply .theta. times .theta. form .theta..sup.2, then multiply f.sub.r
times .theta..sup.2 to form f.sub.r .theta..sup.2. Of course, certain of
these sub-steps can be executed in other than the order shown while still
obtaining the same results.
At Block C the method divides f.sub.r .theta. (formed in sub-step B2) by
2.theta. (formed in sub-step B3) to form f.sub.r .theta./(2.theta.).
At Block D the method subtracts f.sub.r .theta..sup.2 from f.sub.r
.theta./(2.theta.) to form
##EQU4##
At Block E the following operation is performed on the quantities formed
thus far to give:
##EQU5##
The result is the range r of the radiating source relative to the
observer. If desired, an optional smoothing process can be applied to the
range r.
In this case, the quantities representing the frequency rate, the bearing
rate, and the bearing acceleration can be subjected to a smoothing process
to decrease or eliminate rapid fluctuations in the data.
FIG. 2b is a block diagram of an embodiment of a range finder system or
apparatus 10 that operates in accordance with the method illustrated in
the flow chart of FIG. 2a. The range finder apparatus 10 of FIG. 2b is
realizable as a mechanical device, an electrical device, or a digital
device such as a microprocessor. In FIGS. 2b and 3b, the term "amplifier"
is used expressly to identify a device increasing a variable input by a
constant amount, whereas the term "multiplier" is used to identify a
device multiplying two variable inputs; however, it is acknowledged that
the same type of device could be utilized in both instances. The data
inputs include a radiation velocity input 12 receiving the velocity c of
the radiation relative to the medium, a bearing rate input 14 receiving
bearing rate .theta. of the radiating source, a bearing acceleration input
16 receiving bearing acceleration .theta. of the radiating source, a
radiation frequency input be receiving the frequency f.sub.r of the
received radiation, and a radiation frequency change rate input 20
receiving the frequency rate f.sub.r of the radiating source. Data inputs
12, 14, 16, 18 and 20 can be expressed in either a digital representation
or an analog representation. Analog data can be converted to digital data
or vice versa by well known means if the form of the input data is
different from the form of the data required by the processing apparatus.
A first multiplier 22 is provided to receive radiation velocity input 12
and multiply input 12 with radiation frequency change rate input 20 to
obtain cf.sub.r. A second multiplier 24 is provided to multiply frequency
change rate input 20 carrying f.sub.r with bearing acceleration input 16
carrying .theta. to generate a signal of the magnitude f.sub.r .theta.. An
amplifier 26 doubles bearing rate input 14 thereby generating an output of
the magnitude 2.theta. A third multiplier 28 receives bearing rate input
14 and squares the input to generate an output having magnitude
.theta..sup.2. Third multiplier 28 output is connected to one input of a
fourth multiplier 29. The other input of fourth multiplier 29 receives a
signal of magnitude f.sub.r from radiation frequency input 18 and
multiplies the inputs to each other to obtain f.sub.r .theta..sup.2. A
first divider 30 is provided to receive the output from second multiplier
24 and the output from amplifier 26 and divide the second multiplier 24
output by amplifier output 26 to form an output of the magnitude f.sub.r
.theta./(2.theta.). A subtractor 32 is provided to subtract the output of
fourth multiplier 29 from the output of first divider 30 to generate an
output signal having magnitude equal to:
##EQU6##
A second divider 34 is provided to receive the output from first
multiplier 22 and the output from subtractor 32 to divide first multiplier
22 output by subtractor 32 output to generate a range output 36 of
magnitude,
##EQU7##
Output 36 is representative of the range between the target and the
observer. If desired, an optional smoothing process can be applied to
output 36, as described previously.
The alternate method illustrated in the flow chart of FIG. 3a and the
apparatus illustrated in FIG. 3b utilize the fractional frequency rate
F.sub.r instead of the frequency f.sub.r and the frequency rate F.sub.r.
Using the fractional frequency rate is advantageous when the apparatus and
method of the invention is employed with certain types of existing
shipboard equipment that output the fractional frequency rate, instead of
the frequency and frequency rate. The fractional frequency rate is
expressed as
##EQU8##
The second method illustrated in the flow chart of FIG. 3a, and the
corresponding apparatus illustrated in FIG. 3b, utilize the fractional
frequency rate F.sub.r in determining the range of the radiating source
relative to the observer.
At Block A of FIG. 3a there is provided a set of input data. The set of
input data is comprised of the velocity c of the radiation relative to the
medium, the bearing rate .theta. of the radiating source, the bearing
acceleration .theta. of the radiating source, and the fractional frequency
rate F.sub.r of the radiating source.
At Block B the following sub-steps are performed: (B1) multiply c times
F.sub.r to form cF.sub.r ; (B2) multiply F.sub.r times .theta. to form
F.sub.r .theta.; (B3) multiply .theta. times 2 to form 2.theta.; and (B4)
square .theta. to form .theta..sup.2. As before, certain of these steps
can be executed in other than the order shown while still obtaining the
same results.
At Block C the second method divides F.sub.r .theta. (formed in sub-step
B2) by 2.theta. (formed in sub-step B3) to form F.sub.r
.theta./(2.theta.).
At Block D the method subtracts .theta..sup.2 from F.sub.r
.theta./(2.theta.) to form
##EQU9##
At Block E the following operation is performed on the quantities formed
thus far:
##EQU10##
The result is the range r of the radiating source relative to the
observer. If desired, an optional smoothing process can be applied to the
range r.
The quantities representing the frequency rate, the bearing rate, and the
bearing acceleration can be subjected to an optional smoothing process,
such as a moving average, to decrease or eliminate rapid fluctuations in
the data.
FIG. 3b is a block diagram of an embodiment of a range finder system or
apparatus 46 that operates in accordance with the method illustrated in
the flow chart of FIG. 3a. As with the embodiment of FIG. 2b, the range
finder apparatus 46 of FIG. 3b is realizable as a mechanical device, an
electrical device, or as a processing device such as a microprocessor. The
data inputs include a radiation velocity input 42 receiving the velocity c
of the radiation relative to the medium, a bearing rate input 44 receiving
bearing rate .theta. of the radiating source, a bearing acceleration input
46 receiving bearing acceleration .theta. of the radiating source, a
radiation fractional frequency input 48 receiving the fractional frequency
rate F.sub.r of the radiating source. As with the embodiment of FIG. 2b,
data inputs 42, 44, 46, and 48 can be expressed in either a digital
representation or an analog representation, and suitable conversion means
are employed as required in the signal processing blocks.
A first multiplier 56 is provided to receive radiation velocity input 42
and multiply input 42 with radiation fractional frequency input 48 to
obtain cF.sub.r. A second multiplier 52 is provided to multiply radiation
fractional frequency input 48 carrying F.sub.r with bearing acceleration
input 46 carrying .theta. to generate a signal of the magnitude
.theta..sub.r .theta.. An amplifier 54 doubles bearing rate input 44
thereby generating an output of the magnitude 2.theta.. A third multiplier
56 receives bearing rate input 14 and squares the input to generate an
output having magnitude .theta..sup.2. A first divider 58 is provided to
receive the output from second multiplier 52 and the output from amplifier
54 and divide the second multiplier 52 output by amplifier 54 output to
form an output of the magnitude F.sub.r .theta./(2.theta.). A subtractor
60 is provided to subtract the output of third multiplier 56 from the
output of first divider 58 to generate an output signal having magnitude
equal to:
##EQU11##
A second divider 62 is provided to receive the output from first
multiplier 50 and the output from subtractor 60 to divide first multiplier
50 output by subtractor 60 output to generate a range output 64 of
magnitude,
##EQU12##
Output 64 is representative of the range between the target and the
observer. If desired, an optional smoothing process can be applied to the
range r, as described previously.
The range finding apparatus and methods described above may be modified
while still achieving a substantially identical result. Thus, it should be
realized that those having ordinary skill in the art may derive
modifications to the embodiments of the invention disclosed above. The
invention is therefore not to be construed to be limited only to these
disclosed embodiments, but it is instead intended to be limited only as
defined by the breadth and scope of the appended claims.
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